[LeetCode] 1074. 元素和为目标值的子矩阵数量

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[LeetCode] 1074. 元素和为目标值的子矩阵数量

矩阵前缀和.因为矩阵中可能包含负值,所以这题肯定不会存在什么剪枝,动态规划的可能性.所以这个题也就没什么弯弯绕绕.个人感觉算不上个Hard题目. 最直观的思路就是枚举子矩阵,既枚举矩阵的左上角节点和右下角节点所构成的子矩阵.枚举是4层循环. 然后矩阵和的计算是两层循环,肯定不能套在枚举子矩阵的循环里. 我们维护一个矩阵前缀和,即prefix[p][q]是左上角0,0节点和右下角p,q节点构成矩阵的面积和. 那么对于任意矩阵:(i,j)(p,q),其矩阵和 = prefix[p][q] – pre…

python(leetcode)-重复元素算法题

leetcode初级算法问题描述给定一个整数数组,判断是否存在重复元素. 如果任何值在数组中出现至少两次,函数返回 true.如果数组中每个元素都不相同,则返回 false. 该问题表述非常简单查看数组中是否有相同元素解法一:(未通过-超出时间限制) 思路:利用list的内置函数count计算每一个元素的数量如果出现大于1则return True 如果都等于1 return False class Solution: def containsDuplicate(self, nums)…

[LeetCode] Number Of Corner Rectangles 边角矩形的数量

Given a grid where each entry is only 0 or 1, find the number of corner rectangles. A corner rectangle is 4 distinct 1s on the grid that form an axis-aligned rectangle. Note that only the corners need to have the value 1. Also, all four 1s used must…

LeetCode 447. Number of Boomerangs （回力标的数量）

Given n points in the plane that are all pairwise distinct, a "boomerang" is a tuple of points (i, j, k) such that the distance between iand j equals the distance between i and k (the order of the tuple matters). Find the number of boomerangs. Y…

[LeetCode] 305. Number of Islands II 岛屿的数量之二

A 2d grid map of m rows and n columns is initially filled with water. We may perform an addLand operation which turns the water at position (row, col) into a land. Given a list of positions to operate, count the number of islands after each addLand o…

[LeetCode] 305. Number of Islands II 岛屿的数量 II

A 2d grid map of m rows and n columns is initially filled with water. We may perform an addLand operation which turns the water at position (row, col) into a land. Given a list of positions to operate, count the number of islands after each addLand o…